I suspect ALS chose white gold to reduce the overall weight of the timepiece, platinum coupled with the size was considered to be too much of a risk and would attract criticism, so ALS probably played it safe. I also suspect they are saving the platinum version for a Hunderskunt. Plus they probably want to differentiate the triple split from the double split and create enough variation to entice double split owners.
Another “con” which ALS managed to somewhat mitigate is the clasp, which is similar to the one used on various larger models including the Turbograph. It is an engineering marvel and incredibly comfortable to wear. All my larger Patek Grand Complications are less hefty and do not feel as comfortable on the wrist as some of the larger and bulkier ALS timepieces using a clasp. I truly find it more comfortable to wear than any other timepiece I own, even the original 39mm datograph!!